When a computer case has survived several decades from being a new toy through being an unloved relic to being rediscovered and finding its way into the hands of an enthusiast, it is inevitable that it will have picked up some damage along the way. It will be scuffed, maybe cracked, and often broken. If it has faced the ordeal of an international courier after an eBay sale then the likelihood of a break increases significantly.
If you receive a vintage computer in the post and find it cracked or broken, never fear. [Drygol] has a solution, a guide to plastic welding with a soldering iron.
After a thorough cleaning, the technique is to hold the sides of the break together, run the iron along it to melt the plastic together, and scrape the overflowed plastic back into the resulting trench before it solidifies. With careful sanding, a spot of polyester putty, and some spray paint, the broken case can be returned to new condition.
There is a video showing the process, in this case repairing a crack on a Commodore 64 case.
